Literary merit aside, The Da Vinci Code makes huge yet unsupported claims about Christian history. The line between this 'fact' and the fiction it inspires has become blurred precisely because the historical scholarship on which Dan Brown based his narrative is itself pure invention. What is dangerous about the glossy hardbacks claiming new revelations about Jesus's bloodline is that they present themselves as serious historical scholarship. We are moving from a world of fact packaged as entertainment to a world of entertainment packaged as fact.

Thompson calls this sort of bunk 'counterknowledge', and laments the decline in Enlightenment ideals that has allowed the likes of Dr Gillian McKeith to convince thousands of her nutritional genius, and of the difference to their lives her books, DVDs and oatmeal snack bars can make. His book, Counterknowledge, also points the finger at complementary and alternative medicine, bogus historians and media scares.

There is a danger in being so bold - namely, that one begins to sound like a conspiracy theorist oneself. At times, the blistering attacks seem to go too far, and several fairly plausible hypotheses are dismissed out of hand. But desperate times call for a voice like this. After reading this impressive study the reader will be convinced that we are indeed in desperate times.